Various types of internal combustion engines use a common fuel rail to distribute fuel to individual fuel injectors that inject a specified amount of fuel into corresponding intake ports or directly into the cylinders. A fuel injector cup is typically used to couple the upper end of the fuel injector to the fuel rail, with the lower end of the injector being seated into a corresponding bore in the intake manifold or cylinder head. The injector/cup interface includes an upper (fuel) seal, while the injector/bore interface includes a lower (air) seal. An injector retention/orientation clip may be used to facilitate proper positioning of the fuel injector during assembly (and/or maintenance) and to secure the injector to maintain the upper and lower seals during assembly and operation of the engine. Alternatively, a fuel injector/cup assembly may use a “snap fasten” feature to couple the cup to the fuel injector and eliminate the injector clip. Both methods require relatively tight tolerances for the individual components to assure that the overall tolerance stack-up associated with the fuel rail, cup, fuel injector, clip (where present), and intake manifold/cylinder head is controlled to maintain the integrity of the upper and lower seals during operation of the engine.